Soil erosion is a major problem all over the world. It is caused by severe wind and heavy rainfalls that remove fertile soil from agricultural areas. By stabilizing the uppermost layer so it is not easily moved from the earth below by wind or flooding water, large and vulnerable cultural areas can be preserved.
It is known from a number of publications to stabilize earth and subterranean formations by addition or injection of different salt solutions which are precipitated at desired location to cause a binding of loose particles in the formation or earth so that they not easily collapse or are washed out.
Norwegian laid-open publication 313 203 describes a method for precipitating inorganic salts in porous media like e.g. grit formations in unconsolidated hydrocarbon containing reservoirs. According to this method a solution of a first soluble salt is first injected into the formation, then a non-reactive electrolyte is injected followed by a second solution of a second soluble salt, after which, finally, another non-reactive electrolyte is injected. All said solutions/electrolytes are injected to substantially the sae location, namely where the precipitation is desired to take place. To mix the two salt solutions which are both soluble when kept apart from each other but upon mixing cause a desired precipitation, a pump arrangement is required to alternately push and pull the injected solutions and electrolytes until they are thoroughly mixed. Salt solutions described as suitable for the purpose are, as the first solution typically CaCl2 and as the second solution typically KH2PO4, the salt precipitated therefrom being octacalcium-phosphate Ca8H2(PO4)*5H2O. The method has not proved to be effective in full scale, i.a. because the desired pump action is difficult and time consuming and because a high number of repetitive injections are required to achieve the desired stabilizing.
In U.S. Pat. No. 5,143,155 is mentioned that reduction of porosity and permeability of oil reservoirs is possible by precipitating CaCO3 from an aqueous solution containing calcium chloride, urea and urease manufactured bacterial in situ. The object of the patent is to reduce porosity/permeability of geological subterranean formations to increase oil production from an oil reservoir and to reduce the flow of contaminations from previous operation present in the aqueous phase. The '155 patent is not concerned with problems generally related to stabilizing earth (soil) or formations.
It is taught in SPE publications 50621 (Harris, R. E. and McKay, I. D. New application for enzymes in oil and gas production. The 1998 SPE European Petroleum Conference, The Hague, The Netherlands 20-22 Oct. 1998) that urease may be used to decompose urea to consolidate sand when precipitating CaCO3. It is also mentioned in this publication that calcium phosphate can be produced in a reaction between an enzymatically decomposed phosphate and calcium chloride. The publication concludes that such materials have a potential for sealing water conveying layers and for applications related to sand stabilizing.